Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. Freon group of refrigerants are

Toxic

Inflammable

Non-inflammable and toxic

Nontoxic and non-inflammable

2. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant entropy

Takes place at constant temperature

Takes place at constant pressure

Involves no change in volume

3. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

0.2

1.2

4. A thermostatic expansion valve in a refrigeration system

Maintains different temperatures in evaporator in proportion to load

Ensures the evaporator completely filled with refrigerant of the load

None of the above

Is suitable only for constant load systems

5. Highest temperature encountered in refrigeration cycle should be

At critical Temperature

Near critical temperature of refrigerant

Above critical temperature

Much below critical temperature

6. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Unpredictable

Less

Equally

7. The operating pressure for refrigerating units using R-12 as a refrigerant is

15 bar

2 bar

8 bar

30 bar

8. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 1

9: 1

1: 3

1: 9

9. For obtaining high COP, the pressure range of compressor should be

High

Any value

Low

Optimum

10. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

1.33

2.33

3.33

4.33

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11. Critical temperature is the temperature above which

A gas will never liquefy

A gas will immediately liquefy

Water will evaporate

Water will never evaporate

12. The curved lines on a psychrometric chart indicates

Relative humidity

Dry bulb temperature

Wet bulb temperature

Dew point temperature

13. A bootstrap air cooling system has

Four heat exchangers

Three heat exchangers

Two heat exchangers

One heat exchanger

14. The freezing point of sulphur dioxide is

-56.6°C

-77.7°C

-135.8°C

-75.2°C

15. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

2.15

5.12

1.25

16. In a lithium bromide absorption refrigeration system

Lithium bromide is used as a refrigerant and water as an absorbent

Water is used as a refrigerant and lithium bromide as an absorbent

None of these

Ammonia is used as a refrigerant and lithium bromide as an absorbent

17. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Collect liquid refrigerant and prevent it from going to compressor

Collect vapours

Superheat the vapour

Detect liquid in vapour

18. The domestic refrigerator uses following type of compressor

Centrifugal

Axial

Piston type reciprocating

Miniature sealed unit

19. Cooling water is required for following equipment in ammonia absorption plant

Condenser, absorber and separator (rectifier)

Condenser

Absorber

Evaporator

20. The value of C.O.P in vapour compression cycle is usually

Always less than unity

Always more than unity

Equal to unity

Any one of the above

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21. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

(T₁ - T₂)/T₁

T₁ / (T₂ - T₁)

T₂/ (T₂ - T₁)

(T₂ - T₁)/T₁

22. The vapour compression refrigerator employs the following cycle

Reversed Carnot

Carnot

Rankine

Reversed Rankine

23. In a refrigeration system, heat absorbed in comparison to heat rejected is

Less

More for small capacity and less for high capacity

Same

24. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Positive

None of these

Negative

Zero

25. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.376

0.67

0.4

0.6

26. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Super-cooling

None of these

Sub-cooling or under-cooling

Normal cooling

27. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

28. Which of the following is not a desirable property of a refrigerant?

High risibility with oil

Low boiling point

Good electrical conductor

Large latent heat

29. The capillary tube, as an expansion device, is used in

Water coolers

Room air conditioners

All of these

Domestic refrigerators

30. Most thermostatic expansion valves are set for a superheat of

5°C

20°C

15°C

10°C

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31. The minimum temperature to which water can be cooled in a cooling tower is

Dew point temperature of air

Dry bulb temperature of air

Ambient air temperature

Wet bulb temperature of air

32. The bank of tubes at the back of domestic refrigerator is

Refrigerant cooling tubes

Evaporator tubes

Condenser tubes

Capillary tubes

33. The condition of refrigerant after passing through the condenser in a vapour compression system is

Saturated liquid

Dry saturated vapour

Superheated vapour

Wet vapour

34. The boiling point of ammonia is

-77.7°C

-10.5°C

-33.3°C

-30°C

35. Which of the following statement is correct?

(B) The increase in air movement increases the evaporation from the human body.

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(D) Both (A) and (B)

36. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(B) Heat stored in the human body

(D) Difference of (A) and (B)

(A) Heat dissipated to the surroundings

37. Rating of a domestic refrigerator is of the order of

0.1 ton

10 tons

40 tons

5 tons

38. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Freon

Ammonia

Carbon dioxide

Brine

39. In a refrigeration system, the expansion device is connected between the

Condenser and receiver

Compressor and condenser

Receiver and evaporator

Evaporator and compressor

40. Which of the following cycles uses air as the refrigerant?

Bell Coleman

Carnot

Stirling

Ericson

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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